Aspect Ratio Calculator

21:9 Ultrawide Aspect Ratio: Calculator and the Real Panel Ratios

The calculator is preset to 21:9 with a 3440×1440 ultrawide in section 1 — which immediately shows the catch: that panel is 43:18, not 21:9. Below, the exact ratio of every ultrawide resolution and what each one does to 16:9 video.

1 · Find a ratio from pixels

43:18= 2.3889:1 · landscape

Not a standard ratio, but only 0.046% away from 2.39:1 — in practice it will be treated as 2.39:1.

2 · Resize with a locked ratio

Ratio (custom allowed)
:

= 7:3 · 2.3333:1

New size (edit either side)
×

width × height, px

Not a whole pixel: the exact height is 1474.286, shown rounded to 1474 (round-half-to-even). For pixel-perfect results use widths divisible by 7.

3 · Preview: your pixels inside the locked ratio

Content 3440×1440 (43:18) placed in a 7:3 frame:

2.3% of the frame height becomes top/bottom bars.

No ultrawide monitor is exactly 21:9

True 21:9 reduces to 7:3, a decimal of 2.3333. Not one shipping ultrawide resolution matches it. The four panels below span 2.3704 to 2.4000 — all wider than the name suggests, and all different from each other. "21:9" is a category label, not a measurement, and this table is the reason people get confused when a calculator returns 43:18 for their monitor.

Exact ratio = width:height reduced by their GCD. Decimal = width ÷ height, 4 places. Megapixels = width × height ÷ 1,000,000. For comparison, true 21:9 = 7:3 = 2.3333.
Resolution Common name Exact ratio Decimal Megapixels Notes
2560×1080 UW-FHD 64:27 2.3704 2.76 Entry ultrawide; same pixel height as 1080p
3440×1440 UW-QHD 43:18 2.3889 4.95 The most common ultrawide; the closest of the four to 2.39:1 cinema
3840×1600 UW-QHD+ 12:5 2.4000 6.14 Less common; the widest of the four and the only clean 2.4
5120×2160 5K2K / UW-4K 64:27 2.3704 11.06 Ultrawide 4K; same ratio as 2560×1080

Note that 2560×1080 and 5120×2160 share the same ratio, 64:27 — the second is exactly double the first on each side. And 64:27 is not arbitrary: it is precisely (4:3)³, just as 16:9 is precisely (4:3)². Both identities check out exactly, which is why 64:27 turns up in specifications as the "extended" widescreen ratio.

Worked example: 16:9 video on a 3440×1440 ultrawide

A YouTube video is 16:9. Your panel is 43:18. The video is relatively narrower, so it fills the height and gets vertical bars at the sides — pillarboxing. At the full 1440 height the video occupies 1440 × 16 ÷ 9 = 2560 px of width, leaving 3440 − 2560 = 880 px of bars, 440 on each side. That is 25.6% of the panel width.

The pleasant surprise is that 2560×1440 is itself a standard resolution, so a QHD video plays pixel-for-pixel with no scaling at all on an ultrawide. The same is true on 2560×1080, where 16:9 content lands on exactly 1920×1080 with 640 px of bars (25.0%). 3840×1600 is the exception: 16:9 at 1600 tall needs 2844.44 px of width, which is not a whole number, so that panel cannot display 16:9 content on an exact pixel grid. Type those numbers into section 2 above and the tool flags the fractional result directly.

Worked example: why films look right and games look wide

Scope cinema is 2.39:1. On a 3440×1440 panel (2.3889:1) the difference is 0.05%: at full width the film is 1439.33 px tall inside a 1440 px frame, so the letterbox bars total under a single pixel. Films genuinely fill the screen. On 2560×1080 (2.3704) the gap is 0.8% — a thin but real bar.

Games are different because they are not letterboxed at all: a game renders at whatever ratio you give it, so an ultrawide shows more of the world rather than the same view stretched. The reverse is what to watch for — forcing 16:9 content to fill an ultrawide crops 25.6% off its height (1080 becomes 803.7 on 43:18), which is a lot of headroom to lose.

32:9 super ultrawide is a different category

Super ultrawide resolutions. Both are exactly 32:9 — literally two 16:9 screens wide.
Resolution Common name Exact ratio Decimal Equivalent to
3840×1080 DFHD 32:9 3.5556 Two 1920×1080 screens side by side
5120×1440 DQHD 32:9 3.5556 Two 2560×1440 screens side by side

Unlike the 21:9 class, these are exact: 3840 ÷ 1080 and 5120 ÷ 1440 both reduce cleanly to 32:9. No film or video standard is anywhere near 3.5556, so essentially all content on a 32:9 panel is pillarboxed or arranged as two windows side by side.

Related pages

The standard these panels are measured against is covered on the 16:9 resolution chart. To identify what ratio any resolution really is — the same GCD check that turns 3440×1440 into 43:18 — use the pixels-to-ratio lookup. For custom ratios and the letterbox-versus-crop preview in full, go back to the main aspect ratio calculator.

Frequently asked questions

Is any ultrawide monitor actually 21:9?

None of the four standard resolutions is. True 21:9 simplifies to 7:3 (2.3333). Real panels are 64:27 (2.3704) at 2560×1080 and 5120×2160, 43:18 (2.3889) at 3440×1440, and 12:5 (2.4000) at 3840×1600. "21:9" is a marketing label for the whole class — it is memorable and it distinguishes them from 16:9, which is all it was ever meant to do.

Why is 64:27 the ratio that keeps appearing?

64:27 is exactly (4:3)³, and 16:9 is exactly (4:3)². Both are verifiable identities: (4÷3)² = 1.7778 = 16÷9, and (4÷3)³ = 2.3704 = 64÷27. Continuing the same geometric progression from the old 4:3 standard is a tidy way to define a wider format, and 64:27 is sometimes listed in specifications for that reason.

How much of my ultrawide screen do YouTube videos use?

A 16:9 video plays at full height with pillarbox bars down each side. On 2560×1080 that is exactly 1920×1080 of video and 640 px of bars (25% of the width). On 3440×1440 it is exactly 2560×1440 of video and 880 px of bars (25.6%). Both cases are pixel-exact, so the video is not resampled — you just do not fill the whole panel.

Do ultrawide monitors show cinema films without black bars?

Close to it on 3440×1440. Scope films are 2.39:1 and that panel is 2.3889:1 — a 0.05% difference, which works out to bars under one pixel tall in total. Practically speaking the film fills the screen. On 2560×1080 (2.3704) the gap is 0.8%, which is a visible but thin bar. Films shot at 1.85:1 or 16:9 still get side bars on every ultrawide.

Is 32:9 the same thing as 21:9?

No — 32:9 (3.5556) is roughly two 16:9 screens joined edge to edge, which is why 3840×1080 and 5120×1440 are exactly double the width of 1920×1080 and 2560×1440. It is a separate "super ultrawide" category with its own trade-offs, listed in the second table below.